Ring laser gyroscopes are frequently used to sense angular rates in order to guide and navigate a variety of vehicles such as airplanes, rockets, tanks, ships, submarines, drilling rigs, etc. As shown in FIG. 1, a ring laser gyroscope 10 is typically formed of a block 12 of material such as Zerodur® which has a low coefficient of thermal expansion. Accordingly, the block 12 is resistant to expansion over a wide temperature range. The block 12 is provided with an interior passage 14 that communicates with openings at each of its corners. Mirrors 16, 18, and 20 are provided at the corners with one of the mirrors 16, 18, and 20 being used as a read-out device. The interior passage 14 and the mirrors 16, 18, and 20 define a plasma chamber in the form of a closed laser resonant path.
A cathode 22 and anodes 24 and 26 engage corresponding surfaces of the block 12 at openings there through. The cathode 22 and the anodes 24 and 26 are coupled to an electrical source 28 so as to energize gas in order to form a laser plasma in the interior passage 14.
The cathode 22 as shown in FIG. 2 is a standard cathode. The cathode 22 has a dome 30 and a cylindrical wall 32. The dome 30 and the cylindrical wall 32 form a recess 34 that is part of the plasma discharge of the ring laser gyroscope 10. Accordingly, a portion of the plasma enters the recess 34. The cylindrical wall 32 is used to attach the cathode 22 to the block 12 of the ring laser gyroscope 10. The cathode 22 is suitably sealed by a seal 36 to the block 12 in order to contain the gas within the interior passage 14. The seal 36, for example, may be an indium seal. The anodes 24 and 26 may be similarly sealed to the block 12.
Gas ions bombard the cathode 22 during the running of the discharge in the ring laser gyroscope 10. This ion bombardment sputters metal off of the cathode 22. Also, the gas ions are initially held temporarily on the surface of the cathode 22 due to the biasing from the electrical source 28. The metal sputtered from the cathode 22 redeposits on cooler areas of the cathode 22 and on the block 12 next to the cathode 22. As the metal sputtered from the cathode 22 redeposits on the cathode 22, it over coats the gas ions held on the surface of the cathode 22. This trapping of the gas tends to decrease the life of the ring laser gyroscope 10 because it depletes the gas that is available to maintain lasing and the discharge.
The present invention is directed to a cathode design which decreases the current density over the cathode of a gas discharge tube and, therefore, decreases the sputter rate in order to increase the sputter life of a gas discharge tube.